DJ,
The interior is a bit cramped for someone of 360 Spyder's build. The car came with black interior but I reskinned it cream with blue piping to make it feel airier (don't even think that's a word...oh well) with the top on. That said, for a 5'8" 180lb guy the car feels just right.
The pedal arrangement is a bit tight and I would not recommend driving the car with boots or thick soled winter shoes. The gear change is precise and also has the satisfying click clack of the Ferrari gated shifter.
I bought the car used. I used to have a Murcielago but got rid of it. I tried to satiate my hunger for an Italian car with a Porsche C4 Cabrio and then a Turbo. Let's just say that while they are more refined in some ways they definitely don't put a smile on my face the way Lamborghinis do.
The torque is immense in these cars. You have to be concious of clutch use. These cars are notorious for eating up clutches, but I've found that only to be the case when one doesn't know how to handle the left pedal. Any 500+ hp car will eat through clutches like the cookie monster. That said, the acceleration is fierce. There is a very solid and pronounced "kick in the pants" feeling when letting on and off the throttle. More pronounced than most any other street car I've driven, and I've driven just about everything out there including a McLaren F1 (which is one of the few cars that floods the senses in a way the Lamborghini can't).
The car initially feels a bit heavy, but as the speeds escalate, the car seems to shrink around you. Feels very capable. Because of the cab forward design and the steeply straked windshield the car is scary to toss into a corner, but if you do, you come out surprised as to how well mannered the car is. Keep in mind that these cars beat out their Ferrari counterparts and contemporaries in tracks like Hockenheim and the Nurburgring, known for tight turns/handling, and high speed respectively.
The clutch is heavy. A lot more so than the Murcielago. The car also feels "looser" than the Murcielago. Even in open top configuration there is virtually no cowl shake and if you hit over 150mph with the top off it feels like your hair will light on fire at any given moment. The sound from the engine is fantastic and the exhaust note is also nice. Better sounding than the Ferrari 12 in my opinion. That is of course, all things equal, having stock exhaust systems. I drove a 550 Maranello when I was shopping around. Drove my friend's for a few days to see how it would feel too. The Maranello is comparatively bland. Driving a Diablo is almost an event, from the wierd ingress/egress, to the lack of a dead pedal. Performance and "smile on your face" value, the Diablo is also much more car than the Maranello.
The interior trim is very nice and not a stitch out of place. That said, mine has a completely redone interior by some very capable hands. I admit I didn't pay too much attention to the tim in the other Diablos I've driven, but rest assured, nothing glaring, at least not anything a buyer in preliminary stages found. Not as good as the Murcielago, but definitely not what you would expect from a handmade Italian exotic (in a good way). This is also an area of criticism usually in the Lamborghini line, but in my experience it is not applicable to the later cars 97+. I do have a complaint about the seats. They are cossetting but are a bit shaky and definitely look flimsy. When you step out of the car you can shake the damn things on their tracks. I'm thinking of putting some Recaros in there and storing the originals. The engine bay has generous amounts of carbon fiber, which my eyeballs thanked me for after opening the engine bay. Creature comforts are good. I don't listen to the radio, so I can't comment on that. The A/C blows cold, and controls are easy to reach. The warning lights are nicely integrated into the crease on top of the instrument cluster which adds a very nice stealthy and uncluttered look to the interior. The ride height adjustment is a life saver going over speed bumps and the like.
If you drive in the rain DO NOT crack the window open. ALL water within a 50ft radius will magically channel itself into the small opening. Seriously, I think its due to the steeply raked side windows. Especially in the roadsters, which don't have that top metal portion that surrounds the glass. The top of the window glass is very nicely chiseled and shuts snugly. I have not had any problems with water leaking in and I've taken it on an auto car wash (yeah, yeah, drag me to the back and put a bullet in my head, I know). That was the only way to test it since it hasn't really rained much at all in the area. My experience with rain and Diablos was when I was abroad and borrowed my friend's VT for almost 2 weeks. Taking the top off the car can be done by one person but my fear of dropping the top onto the car is deep enough I only do this exercise with help. It stows neatly on top of the engine lid. Good thing is that there is never a shortage of volunteers should you be puttering alone. While it looks like it will kill rear visibility, it hardly affects it. That said, the blind spots are pretty big in these cars, but a swift move of the right ankle remedies that problem in a hurry.
That's the general gist of it. If you have any more specific questions don't hesitate to ask.
Cheers